(1) Field of the Invention
The present invention relates to sealing members to be used in various valves, various pumps and the like, and a process for the formation of such sealing members. The invention also relates to discrete composite ceramic materials comprising pellets which are granular or flaky, and a method for the production thereof.
(2) Related Art Statement
As sealing members for high temperature-high pressure steam valves to be used in thermal power plants, nuclear power plants or the like, coil packings produced by treating asbestos threads with a heat-resistive lubricant and graphite and shaping the thus treated threads in a rectangular section, have been conventionally used, as shown in FIGS. 1A-1C. Coil packing 101 is formed by curving a sealing member 100 shown in FIG. 1A into a circular shape shown in FIG. 1B. Accordingly, a cut 102 exists at one location. A sealing member is formed by stacking a plurality (for example, five to ten) of coil packings as shown in FIG. 1C such that phases of the cuts 102 are staggered from one another, and pressing the piled coil packings with a pressing member (not shown).
However, such a conventional sealing member has the following problems.
(1) First, asbestos is considered a carcinogenic material, and therefore use of asbestos is undesirable for environmental sanitation reasons.
(2) Since the heat-resistive lubricant is consumed over time, the sealing member needs tightening or frequent replacement.
(3) Since many kinds and sizes of valves are used in thermal power plants, nuclear power plants or the like, many kinds of sealing members (packings) having different diameters need to be prepared. However, it is troublesome to control a great many sizes of sealing members, and incorrect selection of the proper sizes is likely unless great care is paid during fitting of the sealing members.
(4) Since a cut is present in one location of the sealing member, it is necessary to carefully set a plurality of such sealing members so that the cuts do not overlap. Such a setting method is difficult and time-consuming. If the sealing members are improperly set, leakage of steam may result.
On the other hand, when discrete ceramic materials made up of granular or flaky ceramic pellets (e.g., alumina) have been used for given purposes, such ceramic materials exhibit typical ceramic features such as heat resistivity and corrosion resistance. However, since such ceramics have great friction resistance, they can be used for limited purposes only, and their use as a sealing member is prohibitive.